Air separation unit and systems incorporating the same

ABSTRACT

A system comprising an air separation unit (ASU) is provided. The ASU is configured to produce liquid nitrogen and pressurize to higher pressure using a pump. ASU may be further configured to produce liquid oxygen that can be directly pressurized to be used in required applications. System may further include oxy-fuel combustion system, integrated gas turbines and integrated enhanced oil and/or gas recovery units. Methods of operating the system included.

BACKGROUND

The invention relates generally to air separation units and systemsincorporating the air separation units. More particularly, the inventionrelates to separation of nitrogen and oxygen from air in liquid form andsystems incorporating these products for use in, for example, suchapplications as power generation and natural resource recovery.

Exhaust streams generated by the combustion of fossil fuels in, forexample, power generation systems, contain nitrogen oxides (NO_(x)) andcarbon monoxide (CO) as byproducts during combustion. A method forachieving near-zero NO_(x), without the need for removal of NO_(x) fromthe exhaust, is the oxy-fuel combustion process. In this method, pureoxygen (typically in combination with a secondary gas such as carbondioxide) is used as the oxidizer, as opposed to using air, therebyresulting in a flue gas with negligible NO_(x) emissions. Additionally,oxy-fuel combustion is an attractive technology for applications, suchas carbon dioxide (CO₂) production or sequestration, that benefit fromproduction of CO₂ with low levels of oxygen contamination. In gasturbines that operate by way of an oxy-fuel process, a CO₂ separationunit is not needed, because the main component of combustion exhaustincludes primarily CO₂, and water (H₂O). By condensing H₂O a highconcentration stream of CO₂ may be produced and can be used for CO₂sequestration or other CO₂ applications.

An air separation unit (ASU) separates oxygen and nitrogen and is usefulas an oxygen source for an oxy-fuel process and for separately providinghigh purity nitrogen. The high purity nitrogen obtained by ASU can beused for any of various applications, such as oil or gas reservoirmanagement in an enhanced oil or gas recovery system, for instance.Nitrogen and carbon dioxide can be used as injection fluids in enhancedoil recovery (EOR). Nitrogen can be an economic alternative to carbondioxide for EOR application.

It is advantageous if the pressure of nitrogen injected into an oil wellis greater than the minimum miscible pressure (MMP) of nitrogen and thatoil. Nitrogen forming a miscible slug with oil aids in freeing the oilfor recovery. Therefore, generally the gaseous low-pressure nitrogensupplied by the ASU is compressed to higher pressure before injectinginto the oil reservoirs. However, in these systems the nitrogenseparated from the oxygen in the ASU is afterwards compressed in gaseousphase to the desired pressure, which demands a significant amount ofpower.

Therefore, there remains a need for a system and method for powergeneration that provides low levels of NOx and CO emissions, along withreduced power consumption.

BRIEF DESCRIPTION

Briefly, in one embodiment, a system is provided. The system includes anair separation unit. The air separation unit includes an air compressionunit configured to produce compressed air at a pressure greater thanabout 3 bars; a heat-exchanger unit configured to receive and cool thecompressed air to produce cooled air; a first distillation unitconfigured to receive the cooled air and produce a first output streamcomprising liquid-nitrogen; and a first pump in direct communicationwith the first distillation unit and configured to pressurize the firstoutput stream to a pressure greater than atmospheric pressure.

In another embodiment, a method is provided. The method includes thesteps of compressing air in an air compression unit to a pressuregreater than about 3 bars; cooling the compressed air by passing througha heat-exchanger unit; distilling the cooled air stream in adistillation unit to produce a first stream comprising liquid-nitrogen,and a second stream; and pressurizing the first stream to a pressuregreater than atmospheric pressure.

In one embodiment, a system is provided. The system includes an airseparation unit and an oil or gas recovery well. The air separation unitincludes an air compression unit configured to produce compressed air ata pressure greater than about 3 bars; a heat-exchanger unit configuredto receive and cool the compressed air to produce cooled air; a firstdistillation unit configured to receive the cooled air and produceliquid-nitrogen; and a first pump in direct communication with the firstdistillation unit and configured to pressurize the liquid-nitrogen to apressure greater than atmospheric pressure. The oil or gas recovery wellis configured to receive the liquid-nitrogen and retrieve the oil orgas.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 illustrates a combined oxy-fuel turbine system;

FIG. 2 is an air separation unit, according to an embodiment of thepresent invention;

FIG. 3 is an air separation unit, according to an embodiment of thepresent invention; and

FIG. 4 illustrates a turbine system, according to another embodiment ofthe invention.

DETAILED DESCRIPTION

Embodiments of the present invention include an ASU that may provideclean, pressurized liquid nitrogen and oxygen output and systemsintegrated with the ASU.

In the following specification and the claims that follow, the singularforms “a”, “an” and “the” include plural referents unless the contextclearly dictates otherwise.

In general, an oxy-fuel combined cycle power plant system 10 includes anair separation unit (ASU) 12, a combustor 14, and a power plant withcooling system 16, as depicted in FIG. 1. The ASU 12 separates oxygenfrom air, providing a supply of oxygen as an oxidizer to the combustor14. The combustor 14 is configured to burn fuel in the presence of thissupplied oxygen, either alone or after mixing with CO₂. Nitrogen fromthe ASU 12 can be stored in a reservoir management unit 18 and/or usedfor other applications, such as, for example, recovering natural gasfrom gas fields or for oil recovery. Products of combustion normallycontain mainly CO₂, H₂O and trace emissions of CO and O₂. The coolingsystem 16 embedded in power plant condenses H₂O from exhaust downstreamof combustor 14, resulting in exhaust gases exceeding 95% CO₂composition.

In one embodiment of the present invention, a system including an ASU isprovided. The ASU is configured to liquefy nitrogen at very lowtemperatures. In one embodiment, the ASU is also configured to liquefyoxygen. The liquid oxygen may be pumped to a pressure suitable foroxy-fuel combustion. Additionally, in some embodiments the liquidnitrogen may be pumped to a very high pressure (300-500 bars) andinjected into an oil/gas reservoir for enhanced oil/gas recovery. Byliquefying both nitrogen and oxygen in the high-pressure ASU, it ispossible to pump them at very low temperatures, thereby increasing theoverall efficiency of the plant compared to existing plants that usegaseous nitrogen and oxygen supplied by low-pressure ASUs.

In one embodiment, the system is configured to produce a carbon dioxidestream from exhaust products of the oxy-fuel combustor. In oneembodiment, the carbon dioxide stream produced here is a high-contentCO₂ stream. As used herein, a “high-content CO₂ stream” is defined as astream having more than about 80% by volume of CO₂. In anotherembodiment, a high-content CO₂ stream contains more than about 90% byvolume of CO₂. In a further embodiment, the high-content CO₂ streamcontains more than about 95% by volume of CO₂. A stream “substantiallyfree of oxygen” is defined as a stream containing less than about 1% byvolume of oxygen. In one embodiment, an oxygen level of less than 10 ppmin the CO₂ exhaust stream is desirable. One example of an applicationwhere a high-content CO₂ stream is desirable is oil recovery fromdepleted oil recovery wells, where CO₂ stream injection is used to forceoil from the well. A portion of the high-content CO₂ exhaust gases mayalso be recirculated to the combustor 14, for mixing with the separatedO₂ from the ASU 12. Maintaining minimum CO emissions from the combustionhelps in maintaining high combustion efficiency.

In one embodiment, system 10 comprises an ASU 12, as shown in FIG. 2.The ASU 12 includes an air compression unit 20; a heat-exchanger unit22; a first distillation unit 26; and a first pump 28. As used herein, a“unit” may be made up of a single component or made up of more than onecomponent. For example, an air compressor unit may be one compressor ormay have more than one compressors combined to produce the required aircompression.

The air compression unit 20 is configured to produce compressed air to apressure greater than about 3 bars. In one embodiment, the aircompression unit 20 is configured to produce a compressed air to apressure greater than about 7 bars. In a further embodiment, the aircompression unit 20 is configured to produce a compressed air at apressure in a range from about 15 bars to about 60 bars. In oneparticular embodiment, the air compression unit 20 is configured toproduce compressed air to a pressure up to about 40 bars. The compressedair passes through the heat-exchanger unit 22, where the air is cooled.The cooling of compressed air is attained by the heat-exchange betweendifferent streams that pass through the heat-exchanger unit 22. Forexample, cool nitrogen and/or oxygen streams separated from air may passthrough the heat-exchanger unit 22 absorbing heat from the compressedair and, thereby, cooling the compressed air.

After passing through the heat-exchanger unit 22, the cooled, compressedair may be subjected to expansion in an expander 24, which further coolsthe already cooled air. In one embodiment, an expander 24 is a valveintroducing a pressure difference to the incoming cooled compressed air.In the expander 24, the cooled compressed air gets expanded suddenly toa lower pressure, resulting in further cooled, reducedpressure-compressed air. In one embodiment, the pressure of thecompressed air, after passing through the expander 24 is less than about5 bars. In one embodiment, the pressure of the air after passing throughthe expander 24 is less than about 3 bars. In one particular embodimentdisclosed further below, the expanded air coming out of the expander 24is at atmospheric pressure.

In one embodiment, the cooled air passed through the expander 24 entersthe first distillation unit 26. In one embodiment, the firstdistillation unit 26 is configured to operate at a pressure greater thanabout 2 bars and is called as a “high-pressure distillation unit”. Inone embodiment, an inlet pressure of the first distillation unit is inthe range from about 3.5 bars to about 5 bars. In one embodiment, thefirst distillation unit 26 operates at atmospheric pressure.

The compressed air entering the first distillation unit 26 is generallyat relatively low temperature. In one embodiment, the temperature of theair entering the first distillation unit 26 is in between about −150° C.and about −210° C. In one further embodiment, the temperature of the airis in the range from about −165° C. to about −185° C.

The temperature of the air entering first distillation unit 26 isdetermined in part by the initial pressure of the compressed air, theability of the heat-exchanger unit 22 to cool the compressed air and theconfiguration of the expander 24 to expand the cooled air. A highpressure compressed air ends up giving out more heat at the time ofexpansion compared to air compressed to a lower pressure. Similarly, aheat-exchanger unit 22 that has low temperature coolant streams willeffectively extract more heat from the compressed air compared to a heatexchanger unit 22 having higher temperature coolant streams. The volume,pressure difference, and the temperature of the expander 24 may changethe heat extracted from the air passing through the expander 24.

In one embodiment, a first output stream 30 produced from the firstdistillation unit 26 comprises liquid nitrogen. In one embodiment, thefirst output stream 30 produced from the first distillation unit 26comprises more than about 25% of the inlet compressed air mass flow andcomprises high purity liquid nitrogen. In one embodiment, the liquidnitrogen of first output stream 30 is of greater than 95% purity. In oneembodiment, the liquid nitrogen is more than about 99% pure. In aparticular embodiment, the liquid nitrogen is of more than 99.9% purity.In one embodiment, the temperature of first output stream 30 producedfrom the first distillation unit 26 is less than about −175° C. In oneembodiment, the temperature of first output stream 30 is less than about−178° C. In one particular embodiment, the temperature of the firstoutput stream 30 is in the range from about −178° C. to about −185° C.

In one embodiment, the pressure of the first output stream 30 is greaterthan atmospheric pressure. In one embodiment, the pressure of the firstoutput stream 30 is greater than about 3 bars. In one particularembodiment, the pressure of the first output stream ranges from about3.5 bars to about 5 bars. Depending on the particular applicationrequirements, in one embodiment, the first output stream 30 is furtherpressurized using a first pump 28. In one embodiment, the first pump 28is in direct communication with the first distillation unit 26. As usedherein the “direct communication” between the pump 28 and distillationunit 26 means that the first output stream 30 from the distillation unit26 is directly pumped to high pressure without intervening expansion orgas-liquid separation. In one embodiment the first output stream 30 ispressurized to greater than about 300 bars. In a further embodiment, thefirst output stream is pressurized to greater than about 400 bars. Inone embodiment, the first output stream 30 is pressurized up to about500 bars. In one embodiment, the first pump 28 is coupled to theheat-exchanger unit 22 so that the first output stream 30 pressurized bythe first pump 28 passes through the heat-exchanger unit 22 therebycooling the incoming compressed air. As used herein “coupled” merelyimplies fluid communication and does not prohibit the usage ofintervening parts such as valves.

The first output stream 30 may be transported for differentapplications. In one embodiment, the first output stream 30 passesthrough the heat-exchanger unit 24, thereby removing some heat from theincoming compressed air from the compressor unit 20. The low-temperatureliquid form of the first output stream 30 is comparatively moreeffective than gaseous nitrogen in reducing the temperature of theincoming compressed air.

After distilling out liquid nitrogen, in one embodiment, thedistillation unit 26 is left with a second output stream 32 thatcomprises nitrogen and oxygen (FIG. 2). The second output stream 32 maybe drawn out from the distillation unit 26 and may be subjected tofurther distillation, using, for example a second distillation unit 36.Depending on the pressure of the second output stream 32, it may befurther subjected to expansion in a second expander 34, as shown in FIG.2. In one embodiment, the outlet pressure of the second expander 34 isnear atmospheric and the temperature of the contents in a range fromabout −190° C. to about −195° C. In one embodiment, the vapor fractionof the output contents of second expander 34 is in the range from about0.12 to 0.18. Depending on the temperature of the second output stream32 and pressure ranges of second expander 34, the stream coming out fromthe second expander 34 may be in a liquid state, gaseous state, or in aliquid-gas mixed state. Therefore, depending on the requirement, thesecond output stream 32 optionally may be subjected to a gas-liquidseparation in a separator 35. In one embodiment, both the gaseous partand liquid part of the second output stream 32 are fed into the seconddistillation column 36. In one embodiment, the second distillation unit36 is a low pressure distillation unit. The pressure at the distillationunit may be less than about 2 bars. In one embodiment, the low pressuredistillation unit 36 works at atmospheric pressure.

The second distillation unit 36 may have one or more outputs. Onedistillation output is third output stream 38 comprising liquid oxygen.In one embodiment, the third output stream 38 is about 15 mass % or moreof the inlet compressed air and comprises high purity liquid oxygen. Inone embodiment, the liquid oxygen of the third output stream 38 is ofgreater than 95% purity. In one embodiment, the liquid oxygen is morethan about 99% pure. In a particular embodiment, the liquid oxygen is ofmore than 99.9% purity. In one embodiment, the temperature of the thirdoutput stream 38 produced at the distillation unit 36 is less than about−175° C. In one embodiment, the temperature of the third output stream38 is less than about −178° C.

In one embodiment, the pressure of third output stream 38 is greaterthan atmospheric pressure. Depending on the particular applicationrequirements, in one embodiment, the third output stream 38 is furtherpressurized using a second pump 39. In one embodiment, the third outputstream 38 is pressurized to greater than about 20 bars. In a furtherembodiment, the third output stream 38 is pressurized in a range fromabout 30 bars to about 60 bars. In a particular embodiment, the thirdoutput stream is pressurized up to about 100 bars of pressure.

The third output stream 38 produced by the distillation may betransported for different applications including oxy-fuel combustion.Similar to the first output stream 30, during conveyance to the intendedapplication, the third output stream 38 may be routed through theheat-exchanger unit 22, thereby helping to remove heat from thecompressed air from the compressor unit 20. The low-temperature liquidform of the third output stream 38 comprising oxygen is comparativelymore effective than the gaseous oxygen in reducing the temperature ofthe incoming compressed air.

In one embodiment, one output of the second distillation unit is afourth output stream 40 comprising nitrogen and oxygen. In oneembodiment, the fourth output stream 40 includes both nitrogen andoxygen in gaseous form. In one embodiment, the temperature of thisstream is about −190° C. In one embodiment, depending on the usage ofsecond expander 34 and/or the distillation conditions at the seconddistillation unit 36, the fourth output stream 40 measures about 40-60%of the inlet compressed air mass flow. In this embodiment, thecomposition of the mixed stream 40 includes about 87 mole % (of fourthoutput stream 40) of nitrogen and 12 mole % of oxygen.

The fourth output stream 40 may be used for different applications,including as an oxidizer in a combustion turbine. For example, if usedin a combustor that generally uses air as an oxidizer, the fourth outputstream 40 will reduce the NOx emission of the combustor. In oneembodiment, the stream 40 may be recycled to the air compression unit 20or to the distillation unit 26.

Similar to the first output stream 30 and third output stream 38, in oneembodiment, the fourth output stream 40 may contribute to the cooling ofcompressed air passing through the heat-exchanger unit 22.

The pressures of compressed air supplied by the compression unit 20, thepressure differences and the resultant cooling obtained through theexpanders 24, 34, and the distillation conditions in the distillationunits 26, 36 may be greatly varied to achieve higher purity, highercontent liquid nitrogen and/or liquid oxygen streams. All suchvariations are believed to be apparent to one skilled in the artconsidering the teachings of this disclosure.

In one variation shown in FIG. 3, compressor unit 20 is configured toproduce compressed air to a pressure greater than about 35 bars. In oneembodiment, the pressure of the compressed air is about 40 bars. Thehigh-pressure compressed air is passed through the heat-exchanger unit22 and cooled. The cooled compressed air from the heat-exchanger unit issubjected to expansion in an expander 24. The heat-exchanger unit 22 asused herein may be one unit or a combination of multiple heat-exchangerunits. In one embodiment, the expander 24 expands the compressed air byquickly reducing pressure (“flashing”) to atmospheric pressure such thatthe air rapidly cools to a liquid form with a temperature less thanabout −185° C. The cooled liquid is subjected to distillation in thefirst distillation unit 26 to directly produce high-purity first outputstream 30 comprising liquid nitrogen and a second output stream 32comprising liquid-oxygen. In one embodiment, both the first outputstream 30 and the second output stream 32 are in liquid forms.Therefore, in one embodiment, the first distillation unit 26 is aliquid-liquid separator. In one particular embodiment, the first outputstream 30 is a liquid nitrogen stream and the second output stream 32 isa liquid oxygen stream. The second output stream comprising liquidoxygen may be further subjected to pressurizing by using a pump 39 andused in different applications.

A number of heat-exchanger units and coolant streams may be effectivelyused to cool the air stream that is subjected to distillation in thefirst distillation unit 26. In one such variation, the incomingcompressed air from the compressor 20 is split in to a first stream 41and a second stream 42 using a splitter 43. The first stream passesthrough a second heat-exchanger unit 44 and third heat-exchanger unit 45to be cooled further. The first stream 41 cooled through the multipleheat-exchangers 44, 45 is expanded in the expander 24. Optionally, thecooled air coming from expander 24 may be subjected to a liquid-gasseparation in a separator 25, using the liquid part for distillationunit 26 and leaving a gaseous waste stream 46 that may be routed throughone or more heat-exchanger units 22, 44, 45 to further cool the incomingcompressed air.

The second stream 42 of the compressed air from splitter 43 may beoptionally used in a turbine 48 and the cooled stream 42 is mixed in amixer 49 with the gaseous waste stream 46. Depending on the temperatureof the second stream 42, the gaseous waste stream 46, and the coolingdemands of the heat-exchangers 44 and 45, the second stream 42 and thegaseous waste stream 46 may be mixed before passing through any of thesecond heat-exchanger units 22, 44, and 45. In one embodiment, thegaseous waste stream 46 is passed through the third heat-exchanger 45and then mixed with the second stream 42 before passing through thesecond heat-exchanger unit 44, thereby effectively cooling the cooledair stream 41 passing from the third heat-exchanger 45 to the expander24.

One particular, advantageous application of the ASUs described above isin the integration of these ASUs to an oxy-fuel gas turbine combinedcycle as shown in FIG. 4. The system 50 includes an ASU 12 providingoxygen output; a combustor 14 configured to receive oxygen from ASU 12and to combust a fuel stream 58, thereby generating a flue gas 62. Inone embodiment, cooling system 16 is fluidly coupled to the combustor 14through a turbine combined cycle 64. The gas turbine combined cycle 64may receive flue gas 62 from the combustor 14, and use at least a partof the energy associated with the flue gas 62 to generate electricity orperform some other work, releasing an exhaust flue gas 66. Exhaust fluegas 66 from the gas turbine combined cycle 64 may be passed through thecooling system 16, such as, for example, a water condensation system orHRSG, to condense water from the exhaust gas 66, and to create a carbondioxide stream 70. The carbon dioxide stream 70 may be stored in astorage unit 72. In another embodiment, the carbon dioxide stream 70 maybe directed to applications that use “high-content” carbon dioxide, suchas for example, a an oil/gas recovery system 78 after optionalcompression in a CO₂ compressor 76. In another embodiment, at least apart of the carbon dioxide stream 70 is redirected to the combustor 14,after optional compression in a CO₂ compressor 76, to be mixed with theoxygen.

In one embodiment, a method of generating energy in a power plant thatincludes a gas turbine is provided. The method includes operating an ASU12 (FIG. 4) to separate oxygen from air, passing fuel to the combustor14, and combusting the fuel stream 58 in the combustor 14, in thepresence of oxygen. In this manner, a flue gas 62 is generated,comprising carbon dioxide and water. The flue gas 62 of the combustor 14may be used in operating the turbine 64, e.g., to generate electricity.The exhaust flue gas 66 of the turbine 64 can be passed through a watercondensation system 16 to separate water from the exhaust gas 66, and toproduce a high-content carbon dioxide stream 70. The high-content carbondioxide stream 70 is substantially free of oxygen, for safetyconsiderations in those situations where the presence of oxygen is aserious concern. As explained above, the carbon dioxide stream 70 may bestored, directed to other applications such as an oil recovery system,and/or compressed and fed back to the combustor 14, e.g., in combinationwith the compressed oxygen.

While the liquid oxygen obtained by the ASU 12 may be pumped to thepressure suitable for oxy-fuel combustion in the combustor 14, theliquid nitrogen may be pumped to a very high pressure (300-500 bars) andcan be injected to the oil/gas recovery system 78. In one embodiment,the oil/gas recovery system 78 is a natural gas recovery system. Thenatural gas 58 recovered from the system 78 may be fed back to thecombustor 14 for the oxy-fuel combustion or stored in a natural gasstoring unit 80 for using in other applications.

Advantageously, liquefying both nitrogen and oxygen in the high-pressureASU as described above allows for these products to be pumped at verylow temperatures, thereby increasing the overall efficiency of thecombined gas turbine plant compared to existing plants that compressnitrogen and oxygen in gaseous phases.

Additionally, as the operation pressure of the ASU (˜3-40 bar) is muchlower than the pressure (300-500 bar) at which the nitrogen is injectedin to the recovery system 78, the system 50 is expected to potentiallyprovide not only a higher overall energy efficiency but also a morecompact and therefore cost-effective design compared to conventionalsystems using a low-pressure ASU. In one embodiment, the powerconsumption of the integrated systems explained herein is about 20% lesscompared to a conventional integrated system.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

1. A system, comprising: an air separation unit (ASU) comprising: an aircompression unit configured to produce compressed air at a pressuregreater than about 3 bars; a heat-exchanger unit configured to receiveand cool the compressed air to produce cooled air; a first distillationunit configured to receive the cooled air and produce a first outputstream comprising liquid-nitrogen; and a first pump in directcommunication with the first distillation unit and configured topressurize the first output stream to a pressure greater thanatmospheric pressure.
 2. The system of claim 1, wherein the first pumpis configured to pressurize the first output stream to a pressure in arange from about 300 bars to about 500 bars.
 3. The system of claim 1,further comprising a natural gas or oil recovery well configured toreceive the first output stream from the first pump.
 4. The system ofclaim 1, wherein the first pump is fluidly coupled to theheat-exchanger.
 5. The system of claim 1, wherein the first distillationunit is configured to produce a second output stream comprising nitrogenand oxygen.
 6. The system of claim 1, wherein the ASU further comprisesa second distillation unit configured to receive the second outputstream from the first distillation unit and produce a third outputstream comprising liquid oxygen.
 7. The system of claim 6, wherein theASU further comprises a second pump in direct communication with thesecond distillation unit and configured to pressurize the third outputstream to a pressure in a range from about 30 bars to about 60 bars. 8.The system of claim 7, wherein the second pump is fluidly coupled to theheat-exchanger.
 9. The system of claim 1, further comprising an oxy-fuelcombustor, configured to receive the third output stream from the ASUand produce a flue gas.
 10. The system of claim 9, further comprising aturbine that is configured to receive the flue gas from combustor andproduce a turbine exhaust flue gas.
 11. The system of claim 10, furthercomprising a condenser configured to receive the turbine exhaust fluegas and produce a carbon dioxide stream.
 12. The system of claim 11,comprising an oil recovery well configured to receive the carbon dioxidestream.
 13. The system of claim 1, wherein the air compression unit isconfigured to produce compressed air at a pressure in a range from about15 bars to about 60 bars.
 14. The system of claim 13, wherein the ASUfurther comprises an expander in fluid communication with heat-exchangerunit and first distillation unit, and configured to expand the cooledair to atmospheric pressure.
 15. A method, comprising: compressing airin an air compression unit to a pressure greater than about 3 bars;cooling the compressed air by passing through a heat-exchanger unit;distilling the cooled air stream in a distillation unit to produce afirst stream comprising liquid-nitrogen, and a second stream; andpressurizing the first stream to a pressure greater than atmosphericpressure.
 16. The method of claim 15, further comprising distilling thesecond stream in a second distillation unit to produce a third streamcomprising liquid oxygen.
 17. The method of claim 16, further comprisingpressurizing the third stream to a pressure in a range from about 30bars to about 60 bars.
 18. The method of claim 15, further comprisingpressurizing the second stream to a pressure in a range from about 30bars to about 60 bars.
 19. A system, comprising: an ASU comprising: anair compression unit configured to produce compressed air at a pressuregreater than about 3 bars; a heat-exchanger unit configured to receiveand cool the compressed air to produce cooled air; a first distillationunit configured to receive the cooled air and produce liquid-nitrogen;and a first pump in direct communication with the first distillationunit and configured to pressurize the liquid-nitrogen to a pressuregreater than atmospheric pressure, and an oil or gas recovery wellconfigured to receive the liquid-nitrogen and retrieve the oil or gas.20. The system of claim 19, wherein the first pump is configured topressurize the liquid nitrogen to a pressure in a range from about 300bars to about 0 500 bars.
 21. The system of claim 19, wherein the ASU isfurther configured to produce liquid oxygen.
 22. The system of claim 21,wherein the ASU comprises a second pump configured to pressurize theliquid-oxygen to a pressure in a range from about 30 bars to about 60bars.
 23. The system of claim 22, further comprising: a combustorconfigured to receive the pressurized liquid oxygen to combust a fuelstream and to produce a flue gas stream; a turbine configured to receivethe flue gas stream to generate electricity and give out the exhaustflue gas; a condenser fluidly-coupled to the turbine, and configured toreceive the exhaust flue gas and produce a carbon dioxide stream; and acompressor configured to compress the carbon dioxide stream.
 24. Thesystem of claim 23, wherein the oil or gas recovery well is furtherconfigured to receive the carbon dioxide stream and retrieve the oil orgas.